With a wind turbine generator that receives energy of wind power with blades to rotate a wind turbine rotor and generates power by driving a generator with the rotation of the wind turbine rotor, there has been a problem in that the output power thereof fluctuates due to fluctuations in wind speed.
As a technology for solving this problem, Patent Literature 1 discloses a wind turbine generator, wherein power of variable frequency generated by a generator, which is connected to a wind turbine shaft, is converted with a rectifier to direct-current power; the direct-current power is converted with an inverter to alternating-current power; a secondary battery that can be charged/discharged is connected in series between the rectifier and the inverter; and the secondary battery is subjected to constant charge/discharge control so as to alleviate fluctuations in the output power to a utility grid. In more detail, the wind turbine generator disclosed in Patent Literature 1 alleviates fluctuations in the output power to the utility grid by using an output value from a high-frequency cut filter, which removes an amount corresponding to the fluctuations from detected value of the output power of the generator, as an output value of the inverter and by absorbing a difference between the generator output power and the inverter output power via charging/discharging of the above-described secondary battery.